1. Field of the Invention
The present invention relates to high-speed data communications cables using at least two twisted pairs of insulated conductors. More particularly, the invention relates to high-speed data communications cables having a light-weight, configurable core-filling isolation pair separator that provides geometrical separation between the twisted pairs of insulated conductors.
2. Discussion of the Related Art
High-speed data communications media in current usage include pairs of insulated conductors twisted together to form a balanced transmission line. Such pairs of insulated conductors are referred to herein as "twisted pairs." Cables for high-speed data communications typically consist of multiple twisted pairs. When twisted pairs are closely placed, such as in a cable, electrical energy may be transferred from one twisted pair of a cable to another twisted pair. Such energy transferred between twisted pairs is referred to as crosstalk. As operating frequencies increase, improved crosstalk isolation between the twisted pairs becomes more critical.
The Telecommunications Industry Association and the Electronics Industry Association (TIA/EIA) have developed standards which specify specific categories of performance for cable impedance, attenuation, skew and particularly crosstalk isolation. One standard for crosstalk or, in particular, crosstalk isolation, is TIA/EIA-568-A, wherein a category 5 cable is required to have 38 dB of isolation between the twisted pairs at 100 MHz and a category 6 cable is required to have 42 dB of isolation between the twisted pairs at 100 MHz. Various cable design techniques have been used to date in order to try to reduce crosstalk and to attempt to meet the industry standards.
For example, one cable implementation known in the industry that has been manufactured and sold as a high-speed data communications cable, includes the twisted pairs formed with relatively tight twists, and the cable is formed into a round construction. In this conventional cable, each twisted pair has a specified distance between twists along a longitudinal direction of the twisted pair, that distance being referred to as the "twist lay." When adjacent twisted pairs have the same twist lay and/or twist direction, they tend to lie within a cable more closely spaced than when the twisted pairs have different twist lays and/or a different twist direction. Such close spacing increases the amount of undesirable crosstalk which occurs between the twisted pairs. In some conventional cables, each twisted pair within the cable has a unique twist lay in order to increase the spacing between pairs and thereby to reduce the crosstalk between twisted pairs of the cable. In addition, the twist direction of the twisted pairs may also be varied. However, this industry standard configuration can only achieve limited crosstalk isolation.
Another cable implementation 100 disclosed in U.S. Pat. No. 4,777,325, is illustrated in FIG. 1, wherein the twisted pairs are enclosed within a jacket 102 that has a wide, flat configuration. In particular, a plurality of twisted pairs 104a-104b, 106a-106b, 108a-108b, and 110a-110b are positioned side-by-side, each in separate compartments 112, 114, 116, and 118 formed within a flat hollow envelope of an extruded outer sheath 120. The cable is provided with separator ribs 122 between a top and a bottom of the sheath to divide the outer sheath into the separate compartments and to prevent lateral movement of the twisted pairs out of their respective compartments. However, one problem with this flat configuration for a cable is that it has limited flexibility as compared to that of a round cable, which hinders installation of the cable in conduits and around bends.
Another cable implementation which addresses the problem of twisted pairs lying too closely together within the cable is described, for example, in U.S. Pat. No. 5,789,711 and is illustrated in FIG. 2. In particular, the cable includes, for example, four twisted pairs 124 disposed about a central pre-shaped support 126, wherein the support positions a twisted pair within grooves or channels 128 formed by the support. In particular, the support provides the grooves or channels which keep the twisted pairs at fixed positions with respect to each other. The support can have any of a number of shapes including, for example, a standard "X", a "+", or the separator as is illustrated in FIG. 2. The prongs or protrusions 130 of the support preserve the geometry of the pairs relative to each other, which helps reduce and stabilize crosstalk between the twisted pairs. However, some problems with the support is that the support adds cost to the cable, may limit the flexibility of the cable and increases the size; e.g., the diameter, of the cable. Another problem may be that the material which forms the support may result in the overall cable being a potential fire and/or smoke hazard.
Still another known industry cable implementation 132 is illustrated in FIG. 3. The cable utilizes a jacket 134 with inward protrusions 136 that form channels 138 within the cable. A twisted pair 140 of conductors 142, 144 is disposed within each channel. The protrusions are used to provide adequate pair separation. However, one problem with these protrusions is that they can be difficult to manufacture. In addition, the protrusions may not provide adequate separation between the twisted pairs where the stability of the protrusions is difficult to provide, and thus performance repeatability of the cable is an issue. Further, another problem is that the jacket is not easily strippable. When the cable is to be stripped by removing the outer jacket, which is often done with a sharp device such as, for example, a razor, the protrusions will not be cut by the incision around the circumference of the jacket and will have to be broken off separately in order to remove the jacket.
Accordingly, some of the problems with the above known configurations are that they are expensive, difficult to use, are generally undesirably large, and have decreased flexibility of the cables and workability of the twisted pairs of wires.